Q: A sample contains $$2.45$$ mol of copper atoms. How many copper atoms are present in the sample? (Avogadro's number $$= 6.022 \times 10$$^{23}$$ atoms/mol)

$$2.45 \times 6.022 \times 10$$^{23}$$ = 1.48 \times 10$$^{24}$$ atoms

Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Atomic mass} = (x_1$)(m_1$) + (x_2$)(m_2$)$$

Question 1

Which of the following best describes a chemical change?

Accepted Answer

Iron rusting when exposed to oxygen.

Question 2

Which law states that matter is neither created nor destroyed in a chemical reaction?

Accepted Answer

Law of Conservation of Mass

Question 3

A sample of water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$\frac{16.0}{2.0} = 8.0$$

Question 4

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 5

A student measures the mass of a sample three times and gets values very close to each other, but far from the true value. This indicates the measurements are:

Accepted Answer

Precise but not accurate.

Question 6

Which of the following is the correct SI base unit for temperature?

Accepted Answer

Kelvin (K)

Question 7

A sample contains $$2.45$$ mol of copper atoms. How many copper atoms are present in the sample? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

$$2.45 	imes 6.022 	imes 10$$^{23}$$ = 1.48 	imes 10$$^{24}$$ atoms

Question 8

Which of the following best explains why sodium metal reacts explosively with water, but sodium ions in table salt are safe to eat?

Accepted Answer

Sodium metal is neutral and highly reactive, while sodium ions have lost an electron and are stable.

Question 9

Which of the following is a derived SI unit?

Accepted Answer

Joule (J)

Question 10

A student needs to convert $$25.0$$ inches to centimeters. Given $$1$$ inch $$= 2.54 cm$$, what is the correct answer with the proper number of significant figures?

Accepted Answer

$$25.0 	imes 2.54 = 63.5 cm$$

Question 11

Which of the following best describes the Law of Multiple Proportions?

Accepted Answer

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

Question 12

Which experiment provided the first evidence that atoms contain smaller, negatively charged particles?

Accepted Answer

Thomson's cathode ray tube experiment

Question 13

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Atomic mass} = (x_1$)(m_1$) + (x_2$)(m_2$)$$

Question 14

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 15

Which of the following is a property of alkali metals?

Accepted Answer

They react explosively with water.

Question 16

A neutral atom of chlorine has 17 protons. How many electrons does it have?

Accepted Answer

17

Question 17

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons and is positively charged.

Question 18

Which of the following is the correct number of significant figures in the measurement $$0.0540$$?

Accepted Answer

3

Question 19

Which of the following best explains why elements heavier than iron are formed in supernovas?

Accepted Answer

Supernovas provide the high energy needed for fusion of lighter elements into heavier ones.

Question 20

Which of the following is the correct relationship for converting grams to moles?

Accepted Answer

$$	ext{moles} = \frac{	ext{grams}}{	ext{molar mass}}$$

Measurement, Physical and Chemical Change, and Energy in Chemistry

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